patch-2.4.15 linux/fs/jbd/transaction.c

• Lines: 2071
• Date: Fri Nov 9 14:25:04 2001
• Orig file: v2.4.14/linux/fs/jbd/transaction.c
• Orig date: Wed Dec 31 16:00:00 1969

diff -u --recursive --new-file v2.4.14/linux/fs/jbd/transaction.c linux/fs/jbd/transaction.c
@@ -0,0 +1,2070 @@
+/*
+ * linux/fs/transaction.c
+ * 
+ * Written by Stephen C. Tweedie <sct@redhat.com>, 1998
+ *
+ * Copyright 1998 Red Hat corp --- All Rights Reserved
+ *
+ * This file is part of the Linux kernel and is made available under
+ * the terms of the GNU General Public License, version 2, or at your
+ * option, any later version, incorporated herein by reference.
+ *
+ * Generic filesystem transaction handling code; part of the ext2fs
+ * journaling system.  
+ *
+ * This file manages transactions (compound commits managed by the
+ * journaling code) and handles (individual atomic operations by the
+ * filesystem).
+ */
+
+#include <linux/sched.h>
+#include <linux/fs.h>
+#include <linux/jbd.h>
+#include <linux/errno.h>
+#include <linux/slab.h>
+#include <linux/locks.h>
+#include <linux/timer.h>
+#include <linux/smp_lock.h>
+#include <linux/mm.h>
+
+extern spinlock_t journal_datalist_lock;
+
+/*
+ * get_transaction: obtain a new transaction_t object.
+ *
+ * Simply allocate and initialise a new transaction.  Create it in
+ * RUNNING state and add it to the current journal (which should not
+ * have an existing running transaction: we only make a new transaction
+ * once we have started to commit the old one).
+ *
+ * Preconditions:
+ *	The journal MUST be locked.  We don't perform atomic mallocs on the
+ *	new transaction	and we can't block without protecting against other
+ *	processes trying to touch the journal while it is in transition.
+ */
+
+static transaction_t * get_transaction (journal_t * journal, int is_try)
+{
+	transaction_t * transaction;
+
+	transaction = jbd_kmalloc (sizeof (transaction_t), GFP_NOFS);
+	if (!transaction)
+		return NULL;
+	
+	memset (transaction, 0, sizeof (transaction_t));
+	
+	transaction->t_journal = journal;
+	transaction->t_state = T_RUNNING;
+	transaction->t_tid = journal->j_transaction_sequence++;
+	transaction->t_expires = jiffies + journal->j_commit_interval;
+
+	/* Set up the commit timer for the new transaction. */
+	J_ASSERT (!journal->j_commit_timer_active);
+	journal->j_commit_timer_active = 1;
+	journal->j_commit_timer->expires = transaction->t_expires;
+	add_timer(journal->j_commit_timer);
+	
+	J_ASSERT (journal->j_running_transaction == NULL);
+	journal->j_running_transaction = transaction;
+
+	return transaction;
+}
+
+/*
+ * Handle management.
+ *
+ * A handle_t is an object which represents a single atomic update to a
+ * filesystem, and which tracks all of the modifications which form part
+ * of that one update.
+ */
+
+/*
+ * start_this_handle: Given a handle, deal with any locking or stalling
+ * needed to make sure that there is enough journal space for the handle
+ * to begin.  Attach the handle to a transaction and set up the
+ * transaction's buffer credits.  
+ */
+
+static int start_this_handle(journal_t *journal, handle_t *handle)
+{
+	transaction_t *transaction;
+	int needed;
+	int nblocks = handle->h_buffer_credits;
+	
+	jbd_debug(3, "New handle %p going live.\n", handle);
+
+repeat:
+
+	lock_journal(journal);
+
+	if (is_journal_aborted(journal) ||
+	    (journal->j_errno != 0 && !(journal->j_flags & JFS_ACK_ERR))) {
+		unlock_journal(journal);
+		return -EROFS; 
+	}
+
+	/* Wait on the journal's transaction barrier if necessary */
+	if (journal->j_barrier_count) {
+		unlock_journal(journal);
+		sleep_on(&journal->j_wait_transaction_locked);
+		goto repeat;
+	}
+	
+repeat_locked:
+	if (!journal->j_running_transaction)
+		get_transaction(journal, 0);
+	/* @@@ Error? */
+	J_ASSERT(journal->j_running_transaction);
+	
+	transaction = journal->j_running_transaction;
+
+	/* If the current transaction is locked down for commit, wait
+	 * for the lock to be released. */
+
+	if (transaction->t_state == T_LOCKED) {
+		unlock_journal(journal);
+		jbd_debug(3, "Handle %p stalling...\n", handle);
+		sleep_on(&journal->j_wait_transaction_locked);
+		goto repeat;
+	}
+	
+	/* If there is not enough space left in the log to write all
+	 * potential buffers requested by this operation, we need to
+	 * stall pending a log checkpoint to free some more log
+	 * space. */
+
+	needed = transaction->t_outstanding_credits + nblocks;
+
+	if (needed > journal->j_max_transaction_buffers) {
+		/* If the current transaction is already too large, then
+		 * start to commit it: we can then go back and attach
+		 * this handle to a new transaction. */
+		
+		jbd_debug(2, "Handle %p starting new commit...\n", handle);
+		log_start_commit(journal, transaction);
+		unlock_journal(journal);
+		sleep_on(&journal->j_wait_transaction_locked);
+		lock_journal(journal);
+		goto repeat_locked;
+	}
+
+	/* 
+	 * The commit code assumes that it can get enough log space
+	 * without forcing a checkpoint.  This is *critical* for
+	 * correctness: a checkpoint of a buffer which is also
+	 * associated with a committing transaction creates a deadlock,
+	 * so commit simply cannot force through checkpoints.
+	 *
+	 * We must therefore ensure the necessary space in the journal
+	 * *before* starting to dirty potentially checkpointed buffers
+	 * in the new transaction. 
+	 *
+	 * The worst part is, any transaction currently committing can
+	 * reduce the free space arbitrarily.  Be careful to account for
+	 * those buffers when checkpointing.
+	 */
+
+	/*
+	 * @@@ AKPM: This seems rather over-defensive.  We're giving commit
+	 * a _lot_ of headroom: 1/4 of the journal plus the size of
+	 * the committing transaction.  Really, we only need to give it
+	 * committing_transaction->t_outstanding_credits plus "enough" for
+	 * the log control blocks.
+	 * Also, this test is inconsitent with the matching one in
+	 * journal_extend().
+	 */
+	needed = journal->j_max_transaction_buffers;
+	if (journal->j_committing_transaction) 
+		needed += journal->j_committing_transaction->
+					t_outstanding_credits;
+	
+	if (log_space_left(journal) < needed) {
+		jbd_debug(2, "Handle %p waiting for checkpoint...\n", handle);
+		log_wait_for_space(journal, needed);
+		goto repeat_locked;
+	}
+
+	/* OK, account for the buffers that this operation expects to
+	 * use and add the handle to the running transaction. */
+
+	handle->h_transaction = transaction;
+	transaction->t_outstanding_credits += nblocks;
+	transaction->t_updates++;
+	transaction->t_handle_count++;
+	jbd_debug(4, "Handle %p given %d credits (total %d, free %d)\n",
+		  handle, nblocks, transaction->t_outstanding_credits,
+		  log_space_left(journal));
+
+	unlock_journal(journal);
+	
+	return 0;
+}
+
+/*
+ * Obtain a new handle.  
+ *
+ * We make sure that the transaction can guarantee at least nblocks of
+ * modified buffers in the log.  We block until the log can guarantee
+ * that much space.  
+ *
+ * This function is visible to journal users (like ext2fs), so is not
+ * called with the journal already locked.
+ *
+ * Return a pointer to a newly allocated handle, or NULL on failure
+ */
+
+handle_t *journal_start(journal_t *journal, int nblocks)
+{
+	handle_t *handle = journal_current_handle();
+	int err;
+	
+	if (!journal)
+		return ERR_PTR(-EROFS);
+
+	if (handle) {
+		J_ASSERT(handle->h_transaction->t_journal == journal);
+		handle->h_ref++;
+		return handle;
+	}
+	
+	handle = jbd_kmalloc(sizeof (handle_t), GFP_NOFS);
+	if (!handle)
+		return ERR_PTR(-ENOMEM);
+	memset (handle, 0, sizeof (handle_t));
+
+	handle->h_buffer_credits = nblocks;
+	handle->h_ref = 1;
+	current->journal_info = handle;
+
+	err = start_this_handle(journal, handle);
+	if (err < 0) {
+		kfree(handle);
+		current->journal_info = NULL;
+		return ERR_PTR(err);
+	}
+
+	return handle;
+}
+
+/*
+ * Return zero on success
+ */
+static int try_start_this_handle(journal_t *journal, handle_t *handle)
+{
+	transaction_t *transaction;
+	int needed;
+	int nblocks = handle->h_buffer_credits;
+	int ret = 0;
+
+	jbd_debug(3, "New handle %p maybe going live.\n", handle);
+
+	lock_journal(journal);
+
+	if (is_journal_aborted(journal) ||
+	    (journal->j_errno != 0 && !(journal->j_flags & JFS_ACK_ERR))) {
+		ret = -EROFS;
+		goto fail_unlock;
+	}
+
+	if (journal->j_barrier_count)
+		goto fail_unlock;
+
+	if (!journal->j_running_transaction && get_transaction(journal, 1) == 0)
+		goto fail_unlock;
+	
+	transaction = journal->j_running_transaction;
+	if (transaction->t_state == T_LOCKED)
+		goto fail_unlock;
+	
+	needed = transaction->t_outstanding_credits + nblocks;
+	/* We could run log_start_commit here */
+	if (needed > journal->j_max_transaction_buffers)
+		goto fail_unlock;
+
+	needed = journal->j_max_transaction_buffers;
+	if (journal->j_committing_transaction) 
+		needed += journal->j_committing_transaction->
+						t_outstanding_credits;
+	
+	if (log_space_left(journal) < needed)
+		goto fail_unlock;
+
+	handle->h_transaction = transaction;
+	transaction->t_outstanding_credits += nblocks;
+	transaction->t_updates++;
+	jbd_debug(4, "Handle %p given %d credits (total %d, free %d)\n",
+		  handle, nblocks, transaction->t_outstanding_credits,
+		  log_space_left(journal));
+	unlock_journal(journal);
+	return 0;
+
+fail_unlock:
+	unlock_journal(journal);
+	if (ret >= 0)
+		ret = -1;
+	return ret;
+}
+
+/*
+ * Try to start a handle, but non-blockingly.  If we weren't able
+ * to, return an ERR_PTR value.
+ */
+handle_t *journal_try_start(journal_t *journal, int nblocks)
+{
+	handle_t *handle = journal_current_handle();
+	int err;
+	
+	if (!journal)
+		return ERR_PTR(-EROFS);
+
+	if (handle) {
+		jbd_debug(4, "h_ref %d -> %d\n",
+				handle->h_ref,
+				handle->h_ref + 1);
+		J_ASSERT(handle->h_transaction->t_journal == journal);
+		if (is_handle_aborted(handle))
+			return ERR_PTR(-EIO);
+		handle->h_ref++;
+		return handle;
+	} else {
+		jbd_debug(4, "no current transaction\n");
+	}
+	
+	if (is_journal_aborted(journal))
+		return ERR_PTR(-EIO);
+	
+	handle = jbd_kmalloc(sizeof (handle_t), GFP_NOFS);
+	if (!handle)
+		return ERR_PTR(-ENOMEM);
+	memset (handle, 0, sizeof (handle_t));
+
+	handle->h_buffer_credits = nblocks;
+	handle->h_ref = 1;
+	current->journal_info = handle;
+
+	err = try_start_this_handle(journal, handle);
+	if (err < 0) {
+		kfree(handle);
+		current->journal_info = NULL;
+		return ERR_PTR(err);
+	}
+
+	return handle;
+}
+
+/*
+ * journal_extend: extend buffer credits.
+ *
+ * Some transactions, such as large extends and truncates, can be done
+ * atomically all at once or in several stages.  The operation requests
+ * a credit for a number of buffer modications in advance, but can
+ * extend its credit if it needs more.  
+ *
+ * journal_extend tries to give the running handle more buffer credits.
+ * It does not guarantee that allocation: this is a best-effort only.
+ * The calling process MUST be able to deal cleanly with a failure to
+ * extend here.
+ *
+ * Return 0 on success, non-zero on failure.
+ *
+ * return code < 0 implies an error
+ * return code > 0 implies normal transaction-full status.
+ */
+
+int journal_extend (handle_t *handle, int nblocks)
+{
+	transaction_t *transaction = handle->h_transaction;
+	journal_t *journal = transaction->t_journal;
+	int result;
+	int wanted;
+
+	lock_journal (journal);
+
+	result = -EIO;
+	if (is_handle_aborted(handle))
+		goto error_out;
+
+	result = 1;
+	       
+	/* Don't extend a locked-down transaction! */
+	if (handle->h_transaction->t_state != T_RUNNING) {
+		jbd_debug(3, "denied handle %p %d blocks: "
+			  "transaction not running\n", handle, nblocks);
+		goto error_out;
+	}
+	
+	wanted = transaction->t_outstanding_credits + nblocks;
+	
+	if (wanted > journal->j_max_transaction_buffers) {
+		jbd_debug(3, "denied handle %p %d blocks: "
+			  "transaction too large\n", handle, nblocks);
+		goto error_out;
+	}
+
+	if (wanted > log_space_left(journal)) {
+		jbd_debug(3, "denied handle %p %d blocks: "
+			  "insufficient log space\n", handle, nblocks);
+		goto error_out;
+	}
+	
+	handle->h_buffer_credits += nblocks;
+	transaction->t_outstanding_credits += nblocks;
+	result = 0;
+
+	jbd_debug(3, "extended handle %p by %d\n", handle, nblocks);
+	
+error_out:
+	unlock_journal (journal);
+	return result;
+}
+
+
+/*
+ * journal_restart: restart a handle for a multi-transaction filesystem
+ * operation.
+ *
+ * If the journal_extend() call above fails to grant new buffer credits
+ * to a running handle, a call to journal_restart will commit the
+ * handle's transaction so far and reattach the handle to a new
+ * transaction capabable of guaranteeing the requested number of
+ * credits.
+ */
+
+int journal_restart(handle_t *handle, int nblocks)
+{
+	transaction_t *transaction = handle->h_transaction;
+	journal_t *journal = transaction->t_journal;
+	int ret;
+
+	/* If we've had an abort of any type, don't even think about
+	 * actually doing the restart! */
+	if (is_handle_aborted(handle))
+		return 0;
+	
+	/* First unlink the handle from its current transaction, and
+	 * start the commit on that. */
+	
+	J_ASSERT (transaction->t_updates > 0);
+	J_ASSERT (journal_current_handle() == handle);
+
+	transaction->t_outstanding_credits -= handle->h_buffer_credits;
+	transaction->t_updates--;
+
+	if (!transaction->t_updates)
+		wake_up(&journal->j_wait_updates);
+
+	jbd_debug(2, "restarting handle %p\n", handle);
+	log_start_commit(journal, transaction);
+
+	handle->h_buffer_credits = nblocks;
+	ret = start_this_handle(journal, handle);
+	return ret;
+}
+
+
+/* 
+ * Barrier operation: establish a transaction barrier. 
+ *
+ * This locks out any further updates from being started, and blocks
+ * until all existing updates have completed, returning only once the
+ * journal is in a quiescent state with no updates running.
+ *
+ * The journal lock should not be held on entry.
+ */
+
+void journal_lock_updates (journal_t *journal)
+{
+	lock_journal(journal);
+	++journal->j_barrier_count;
+
+	/* Wait until there are no running updates */
+	while (1) {
+		transaction_t *transaction = journal->j_running_transaction;
+		if (!transaction)
+			break;
+		if (!transaction->t_updates)
+			break;
+		
+		unlock_journal(journal);
+		sleep_on(&journal->j_wait_updates);
+		lock_journal(journal);
+	}
+
+	unlock_journal(journal);
+
+	/* We have now established a barrier against other normal
+	 * updates, but we also need to barrier against other
+	 * journal_lock_updates() calls to make sure that we serialise
+	 * special journal-locked operations too. */
+	down(&journal->j_barrier);
+}
+
+/*
+ * Release a transaction barrier obtained with journal_lock_updates().
+ *
+ * Should be called without the journal lock held.
+ */
+
+void journal_unlock_updates (journal_t *journal)
+{
+	lock_journal(journal);
+
+	J_ASSERT (journal->j_barrier_count != 0);
+	
+	up(&journal->j_barrier);
+	--journal->j_barrier_count;
+	wake_up(&journal->j_wait_transaction_locked);
+	unlock_journal(journal);
+}
+
+/*
+ * journal_get_write_access: notify intent to modify a buffer for metadata
+ * (not data) update.
+ *
+ * If the buffer is already part of the current transaction, then there
+ * is nothing we need to do.  If it is already part of a prior
+ * transaction which we are still committing to disk, then we need to
+ * make sure that we do not overwrite the old copy: we do copy-out to
+ * preserve the copy going to disk.  We also account the buffer against
+ * the handle's metadata buffer credits (unless the buffer is already
+ * part of the transaction, that is).
+ *
+ * Returns an error code or 0 on success.
+ *
+ * In full data journalling mode the buffer may be of type BJ_AsyncData,
+ * because we're write()ing a buffer which is also part of a shared mapping.
+ */
+
+static int
+do_get_write_access(handle_t *handle, struct journal_head *jh, int force_copy) 
+{
+	transaction_t *transaction = handle->h_transaction;
+	journal_t *journal = transaction->t_journal;
+	int error;
+	char *frozen_buffer = NULL;
+	int need_copy = 0;
+
+	jbd_debug(5, "buffer_head %p, force_copy %d\n", jh, force_copy);
+
+	JBUFFER_TRACE(jh, "entry");
+repeat:
+	/* @@@ Need to check for errors here at some point. */
+
+	/*
+	 * AKPM: neither bdflush nor kupdate run with the BKL.   There's
+	 * nothing we can do to prevent them from starting writeout of a
+	 * BUF_DIRTY buffer at any time.  And checkpointing buffers are on
+	 * BUF_DIRTY.  So.  We no longer assert that the buffer is unlocked.
+	 *
+	 * However.  It is very wrong for us to allow ext3 to start directly
+	 * altering the ->b_data of buffers which may at that very time be
+	 * undergoing writeout to the client filesystem.  This can leave
+	 * the filesystem in an inconsistent, transient state if we crash.
+	 * So what we do is to steal the buffer if it is in checkpoint
+	 * mode and dirty.  The journal lock will keep out checkpoint-mode
+	 * state transitions within journal_remove_checkpoint() and the buffer
+	 * is locked to keep bdflush/kupdate/whoever away from it as well.
+	 *
+	 * AKPM: we have replaced all the lock_journal_bh_wait() stuff with a
+	 * simple lock_journal().  This code here will care for locked buffers.
+	 */
+	/*
+	 * The buffer_locked() || buffer_dirty() tests here are simply an
+	 * optimisation tweak.  If anyone else in the system decides to
+	 * lock this buffer later on, we'll blow up.  There doesn't seem
+	 * to be a good reason why they should do this.
+	 */
+	if (jh->b_cp_transaction &&
+	    (buffer_locked(jh2bh(jh)) || buffer_dirty(jh2bh(jh)))) {
+		unlock_journal(journal);
+		lock_buffer(jh2bh(jh));
+		spin_lock(&journal_datalist_lock);
+		if (jh->b_cp_transaction && buffer_dirty(jh2bh(jh))) {
+			/* OK, we need to steal it */
+			JBUFFER_TRACE(jh, "stealing from checkpoint mode");
+			J_ASSERT_JH(jh, jh->b_next_transaction == NULL);
+			J_ASSERT_JH(jh, jh->b_frozen_data == NULL);
+
+			J_ASSERT(handle->h_buffer_credits > 0);
+			handle->h_buffer_credits--;
+
+			/* This will clear BH_Dirty and set BH_JBDDirty. */
+			JBUFFER_TRACE(jh, "file as BJ_Reserved");
+			__journal_file_buffer(jh, transaction, BJ_Reserved);
+
+			/* And pull it off BUF_DIRTY, onto BUF_CLEAN */
+			refile_buffer(jh2bh(jh));
+
+			/*
+			 * The buffer is now hidden from bdflush.   It is
+			 * metadata against the current transaction.
+			 */
+			JBUFFER_TRACE(jh, "steal from cp mode is complete");
+		}
+		spin_unlock(&journal_datalist_lock);
+		unlock_buffer(jh2bh(jh));
+		lock_journal(journal);
+	}
+
+	J_ASSERT_JH(jh, !buffer_locked(jh2bh(jh)));
+
+	error = -EROFS;
+	if (is_handle_aborted(handle)) 
+		goto out_unlocked;
+	error = 0;
+
+	spin_lock(&journal_datalist_lock);
+
+	/* The buffer is already part of this transaction if
+	 * b_transaction or b_next_transaction points to it. */
+
+	if (jh->b_transaction == transaction ||
+	    jh->b_next_transaction == transaction)
+		goto done_locked;
+
+	/* If there is already a copy-out version of this buffer, then
+	 * we don't need to make another one. */
+
+	if (jh->b_frozen_data) {
+		JBUFFER_TRACE(jh, "has frozen data");
+		J_ASSERT_JH(jh, jh->b_next_transaction == NULL);
+		jh->b_next_transaction = transaction;
+
+		J_ASSERT_JH(jh, handle->h_buffer_credits > 0);
+		handle->h_buffer_credits--;
+		goto done_locked;
+	}
+	
+	/* Is there data here we need to preserve? */
+
+	if (jh->b_transaction && jh->b_transaction != transaction) {
+		JBUFFER_TRACE(jh, "owned by older transaction");
+		J_ASSERT_JH(jh, jh->b_next_transaction == NULL);
+		J_ASSERT_JH(jh, jh->b_transaction ==
+					journal->j_committing_transaction);
+
+		/* There is one case we have to be very careful about.
+		 * If the committing transaction is currently writing
+		 * this buffer out to disk and has NOT made a copy-out,
+		 * then we cannot modify the buffer contents at all
+		 * right now.  The essence of copy-out is that it is the
+		 * extra copy, not the primary copy, which gets
+		 * journaled.  If the primary copy is already going to
+		 * disk then we cannot do copy-out here. */
+
+		if (jh->b_jlist == BJ_Shadow) {
+			JBUFFER_TRACE(jh, "on shadow: sleep");
+			spin_unlock(&journal_datalist_lock);
+			unlock_journal(journal);
+			/* commit wakes up all shadow buffers after IO */
+			sleep_on(&jh2bh(jh)->b_wait);
+			lock_journal(journal);
+			goto repeat;
+		}
+			
+		/* Only do the copy if the currently-owning transaction
+		 * still needs it.  If it is on the Forget list, the
+		 * committing transaction is past that stage.  The
+		 * buffer had better remain locked during the kmalloc,
+		 * but that should be true --- we hold the journal lock
+		 * still and the buffer is already on the BUF_JOURNAL
+		 * list so won't be flushed. 
+		 *
+		 * Subtle point, though: if this is a get_undo_access,
+		 * then we will be relying on the frozen_data to contain
+		 * the new value of the committed_data record after the
+		 * transaction, so we HAVE to force the frozen_data copy
+		 * in that case. */
+
+		if (jh->b_jlist != BJ_Forget || force_copy) {
+			JBUFFER_TRACE(jh, "generate frozen data");
+			if (!frozen_buffer) {
+				JBUFFER_TRACE(jh, "allocate memory for buffer");
+				spin_unlock(&journal_datalist_lock);
+				unlock_journal(journal);
+				frozen_buffer = jbd_kmalloc(jh2bh(jh)->b_size,
+							    GFP_NOFS);
+				lock_journal(journal);
+				if (!frozen_buffer) {
+					printk(KERN_EMERG __FUNCTION__
+						"OOM for frozen_buffer\n");
+					JBUFFER_TRACE(jh, "oom!");
+					error = -ENOMEM;
+					spin_lock(&journal_datalist_lock);
+					goto done_locked;
+				}
+				goto repeat;
+			}
+
+			jh->b_frozen_data = frozen_buffer;
+			frozen_buffer = NULL;
+			need_copy = 1;
+		}
+		jh->b_next_transaction = transaction;
+	}
+
+	J_ASSERT(handle->h_buffer_credits > 0);
+	handle->h_buffer_credits--;
+
+	/* Finally, if the buffer is not journaled right now, we need to
+	 * make sure it doesn't get written to disk before the caller
+	 * actually commits the new data. */
+
+	if (!jh->b_transaction) {
+		JBUFFER_TRACE(jh, "no transaction");
+		J_ASSERT_JH(jh, !jh->b_next_transaction);
+		jh->b_transaction = transaction;
+		JBUFFER_TRACE(jh, "file as BJ_Reserved");
+		__journal_file_buffer(jh, transaction, BJ_Reserved);
+	}
+	
+done_locked:
+	spin_unlock(&journal_datalist_lock);
+	if (need_copy) {
+		struct page *page;
+		int offset;
+		char *source;
+
+		J_ASSERT_JH(jh, buffer_uptodate(jh2bh(jh)));
+		page = jh2bh(jh)->b_page;
+		offset = ((unsigned long) jh2bh(jh)->b_data) & ~PAGE_MASK;
+		source = kmap(page);
+		memcpy(jh->b_frozen_data, source+offset, jh2bh(jh)->b_size);
+		kunmap(page);
+	}
+	
+
+	/* If we are about to journal a buffer, then any revoke pending
+           on it is no longer valid. */
+	journal_cancel_revoke(handle, jh);
+
+out_unlocked:
+	if (frozen_buffer)
+		kfree(frozen_buffer);
+
+	JBUFFER_TRACE(jh, "exit");
+	return error;
+}
+
+int journal_get_write_access (handle_t *handle, struct buffer_head *bh) 
+{
+	transaction_t *transaction = handle->h_transaction;
+	journal_t *journal = transaction->t_journal;
+	struct journal_head *jh = journal_add_journal_head(bh);
+	int rc;
+
+	/* We do not want to get caught playing with fields which the
+	 * log thread also manipulates.  Make sure that the buffer
+	 * completes any outstanding IO before proceeding. */
+	lock_journal(journal);
+	rc = do_get_write_access(handle, jh, 0);
+	journal_unlock_journal_head(jh);
+	unlock_journal(journal);
+	return rc;
+}
+
+
+/*
+ * When the user wants to journal a newly created buffer_head
+ * (ie. getblk() returned a new buffer and we are going to populate it
+ * manually rather than reading off disk), then we need to keep the
+ * buffer_head locked until it has been completely filled with new
+ * data.  In this case, we should be able to make the assertion that
+ * the bh is not already part of an existing transaction.  
+ * 
+ * The buffer should already be locked by the caller by this point.
+ * There is no lock ranking violation: it was a newly created,
+ * unlocked buffer beforehand. */
+
+int journal_get_create_access (handle_t *handle, struct buffer_head *bh) 
+{
+	transaction_t *transaction = handle->h_transaction;
+	journal_t *journal = transaction->t_journal;
+	struct journal_head *jh = journal_add_journal_head(bh);
+	int err;
+	
+	jbd_debug(5, "journal_head %p\n", jh);
+	lock_journal(journal);
+	err = -EROFS;
+	if (is_handle_aborted(handle))
+		goto out;
+	err = 0;
+	
+	JBUFFER_TRACE(jh, "entry");
+	/* The buffer may already belong to this transaction due to
+	 * pre-zeroing in the filesystem's new_block code.  It may also
+	 * be on the previous, committing transaction's lists, but it
+	 * HAS to be in Forget state in that case: the transaction must
+	 * have deleted the buffer for it to be reused here. */
+	J_ASSERT_JH(jh, (jh->b_transaction == transaction ||
+			 jh->b_transaction == NULL ||
+			 (jh->b_transaction == journal->j_committing_transaction &&
+			  jh->b_jlist == BJ_Forget)));
+
+	J_ASSERT_JH(jh, jh->b_next_transaction == NULL);
+	J_ASSERT_JH(jh, buffer_locked(jh2bh(jh)));
+
+	J_ASSERT_JH(jh, handle->h_buffer_credits > 0);
+	handle->h_buffer_credits--;
+
+	spin_lock(&journal_datalist_lock);
+	if (jh->b_transaction == NULL) {
+		jh->b_transaction = transaction;
+		JBUFFER_TRACE(jh, "file as BJ_Reserved");
+		__journal_file_buffer(jh, transaction, BJ_Reserved);
+		JBUFFER_TRACE(jh, "refile");
+		refile_buffer(jh2bh(jh));
+	} else if (jh->b_transaction == journal->j_committing_transaction) {
+		JBUFFER_TRACE(jh, "set next transaction");
+		jh->b_next_transaction = transaction;
+	}
+	spin_unlock(&journal_datalist_lock);
+
+	/*
+	 * akpm: I added this.  ext3_alloc_branch can pick up new indirect
+	 * blocks which contain freed but then revoked metadata.  We need
+	 * to cancel the revoke in case we end up freeing it yet again
+	 * and the reallocating as data - this would cause a second revoke,
+	 * which hits an assertion error.
+	 */
+	JBUFFER_TRACE(jh, "cancelling revoke");
+	journal_cancel_revoke(handle, jh);
+	journal_unlock_journal_head(jh);
+out:
+	unlock_journal(journal);
+	return err;
+}
+
+
+
+/*
+ * journal_get_undo_access: Notify intent to modify metadata with non-
+ * rewindable consequences
+ *
+ * Sometimes there is a need to distinguish between metadata which has
+ * been committed to disk and that which has not.  The ext3fs code uses
+ * this for freeing and allocating space: we have to make sure that we
+ * do not reuse freed space until the deallocation has been committed,
+ * since if we overwrote that space we would make the delete
+ * un-rewindable in case of a crash.
+ * 
+ * To deal with that, journal_get_undo_access requests write access to a
+ * buffer for parts of non-rewindable operations such as delete
+ * operations on the bitmaps.  The journaling code must keep a copy of
+ * the buffer's contents prior to the undo_access call until such time
+ * as we know that the buffer has definitely been committed to disk.
+ * 
+ * We never need to know which transaction the committed data is part
+ * of: buffers touched here are guaranteed to be dirtied later and so
+ * will be committed to a new transaction in due course, at which point
+ * we can discard the old committed data pointer.
+ *
+ * Returns error number or 0 on success.  
+ */
+
+int journal_get_undo_access (handle_t *handle, struct buffer_head *bh)
+{
+	journal_t *journal = handle->h_transaction->t_journal;
+	int err;
+	struct journal_head *jh = journal_add_journal_head(bh);
+
+	JBUFFER_TRACE(jh, "entry");
+	lock_journal(journal);
+
+	/* Do this first --- it can drop the journal lock, so we want to
+	 * make sure that obtaining the committed_data is done
+	 * atomically wrt. completion of any outstanding commits. */
+	err = do_get_write_access (handle, jh, 1);
+	if (err)
+		goto out;
+	
+	if (!jh->b_committed_data) {
+		/* Copy out the current buffer contents into the
+		 * preserved, committed copy. */
+		JBUFFER_TRACE(jh, "generate b_committed data");
+		jh->b_committed_data = jbd_kmalloc(jh2bh(jh)->b_size, 
+						   GFP_NOFS);
+		if (!jh->b_committed_data) {
+			printk(KERN_EMERG __FUNCTION__
+				": No memory for committed data!\n");
+			err = -ENOMEM;
+			goto out;
+		}
+		
+		memcpy (jh->b_committed_data, jh2bh(jh)->b_data,
+				jh2bh(jh)->b_size);
+	}
+
+out:
+	if (!err)
+		J_ASSERT_JH(jh, jh->b_committed_data);
+	journal_unlock_journal_head(jh);
+	unlock_journal(journal);
+	return err;
+}
+
+/* 
+ * journal_dirty_data: mark a buffer as containing dirty data which
+ * needs to be flushed before we can commit the current transaction.  
+ *
+ * The buffer is placed on the transaction's data list and is marked as
+ * belonging to the transaction.
+ *
+ * If `async' is set then the writebask will be initiated by the caller
+ * using submit_bh -> end_buffer_io_async.  We put the buffer onto
+ * t_async_datalist.
+ * 
+ * Returns error number or 0 on success.  
+ *
+ * journal_dirty_data() can be called via page_launder->ext3_writepage
+ * by kswapd.  So it cannot block.  Happily, there's nothing here
+ * which needs lock_journal if `async' is set.
+ *
+ * When the buffer is on the current transaction we freely move it
+ * between BJ_AsyncData and BJ_SyncData according to who tried to
+ * change its state last.
+ */
+
+int journal_dirty_data (handle_t *handle, struct buffer_head *bh, int async)
+{
+	journal_t *journal = handle->h_transaction->t_journal;
+	int need_brelse = 0;
+	int wanted_jlist = async ? BJ_AsyncData : BJ_SyncData;
+	struct journal_head *jh;
+
+	if (is_handle_aborted(handle))
+		return 0;
+	
+	jh = journal_add_journal_head(bh);
+	JBUFFER_TRACE(jh, "entry");
+
+	/*
+	 * The buffer could *already* be dirty.  Writeout can start
+	 * at any time.
+	 */
+	jbd_debug(4, "jh: %p, tid:%d\n", jh, handle->h_transaction->t_tid);
+
+	/*
+	 * What if the buffer is already part of a running transaction?
+	 * 
+	 * There are two cases:
+	 * 1) It is part of the current running transaction.  Refile it,
+	 *    just in case we have allocated it as metadata, deallocated
+	 *    it, then reallocated it as data. 
+	 * 2) It is part of the previous, still-committing transaction.
+	 *    If all we want to do is to guarantee that the buffer will be
+	 *    written to disk before this new transaction commits, then
+	 *    being sure that the *previous* transaction has this same 
+	 *    property is sufficient for us!  Just leave it on its old
+	 *    transaction.
+	 *
+	 * In case (2), the buffer must not already exist as metadata
+	 * --- that would violate write ordering (a transaction is free
+	 * to write its data at any point, even before the previous
+	 * committing transaction has committed).  The caller must
+	 * never, ever allow this to happen: there's nothing we can do
+	 * about it in this layer.
+	 */
+	spin_lock(&journal_datalist_lock);
+	if (jh->b_transaction) {
+		JBUFFER_TRACE(jh, "has transaction");
+		if (jh->b_transaction != handle->h_transaction) {
+			JBUFFER_TRACE(jh, "belongs to older transaction");
+			J_ASSERT_JH(jh, jh->b_transaction ==
+					journal->j_committing_transaction);
+
+			/* @@@ IS THIS TRUE  ? */
+			/*
+			 * Not any more.  Scenario: someone does a write()
+			 * in data=journal mode.  The buffer's transaction has
+			 * moved into commit.  Then someone does another
+			 * write() to the file.  We do the frozen data copyout
+			 * and set b_next_transaction to point to j_running_t.
+			 * And while we're in that state, someone does a
+			 * writepage() in an attempt to pageout the same area
+			 * of the file via a shared mapping.  At present that
+			 * calls journal_dirty_data(), and we get right here.
+			 * It may be too late to journal the data.  Simply
+			 * falling through to the next test will suffice: the
+			 * data will be dirty and wil be checkpointed.  The
+			 * ordering comments in the next comment block still
+			 * apply.
+			 */
+			//J_ASSERT_JH(jh, jh->b_next_transaction == NULL);
+
+			/*
+			 * If we're journalling data, and this buffer was
+			 * subject to a write(), it could be metadata, forget
+			 * or shadow against the committing transaction.  Now,
+			 * someone has dirtied the same darn page via a mapping
+			 * and it is being writepage()'d.
+			 * We *could* just steal the page from commit, with some
+			 * fancy locking there.  Instead, we just skip it -
+			 * don't tie the page's buffers to the new transaction
+			 * at all.
+			 * Implication: if we crash before the writepage() data
+			 * is written into the filesystem, recovery will replay
+			 * the write() data.
+			 */
+			if (jh->b_jlist != BJ_None &&
+					jh->b_jlist != BJ_SyncData &&
+					jh->b_jlist != BJ_AsyncData) {
+				JBUFFER_TRACE(jh, "Not stealing");
+				goto no_journal;
+			}
+
+			/*
+			 * This buffer may be undergoing writeout in commit.  We
+			 * can't return from here and let the caller dirty it
+			 * again because that can cause the write-out loop in
+			 * commit to never terminate.
+			 */
+			if (!async && buffer_dirty(bh)) {
+				atomic_inc(&bh->b_count);
+				spin_unlock(&journal_datalist_lock);
+				need_brelse = 1;
+				ll_rw_block(WRITE, 1, &bh);
+				wait_on_buffer(bh);
+				spin_lock(&journal_datalist_lock);
+				/* The buffer may become locked again at any
+				   time if it is redirtied */
+			}
+
+			/* journal_clean_data_list() may have got there first */
+			if (jh->b_transaction != NULL) {
+				JBUFFER_TRACE(jh, "unfile from commit");
+				__journal_unfile_buffer(jh);
+				jh->b_transaction = NULL;
+			}
+			/* The buffer will be refiled below */
+
+		}
+		/*
+		 * Special case --- the buffer might actually have been
+		 * allocated and then immediately deallocated in the previous,
+		 * committing transaction, so might still be left on that
+		 * transaction's metadata lists.
+		 */
+		if (jh->b_jlist != wanted_jlist) {
+			JBUFFER_TRACE(jh, "not on correct data list: unfile");
+			J_ASSERT_JH(jh, jh->b_jlist != BJ_Shadow);
+			__journal_unfile_buffer(jh);
+			jh->b_transaction = NULL;
+			JBUFFER_TRACE(jh, "file as data");
+			__journal_file_buffer(jh, handle->h_transaction,
+						wanted_jlist);
+		}
+	} else {
+		JBUFFER_TRACE(jh, "not on a transaction");
+		__journal_file_buffer(jh, handle->h_transaction, wanted_jlist);
+	}
+	/*
+	 * We need to mark the buffer dirty and refile it inside the lock to
+	 * protect it from release by journal_try_to_free_buffer()
+	 *
+	 * We set ->b_flushtime to something small enough to typically keep
+	 * kupdate away from the buffer.
+	 *
+	 * We don't need to do a balance_dirty() - __block_commit_write()
+	 * does that.
+	 */
+	if (!async && !atomic_set_buffer_dirty(jh2bh(jh))) {
+		jh2bh(jh)->b_flushtime =
+			jiffies + journal->j_commit_interval + 1 * HZ;
+		refile_buffer(jh2bh(jh));
+	}
+no_journal:
+	spin_unlock(&journal_datalist_lock);
+	if (need_brelse) {
+		BUFFER_TRACE(bh, "brelse");
+		__brelse(bh);
+	}
+	JBUFFER_TRACE(jh, "exit");
+	journal_unlock_journal_head(jh);
+	return 0;
+}
+
+/* 
+ * journal_dirty_metadata: mark a buffer as containing dirty metadata
+ * which needs to be journaled as part of the current transaction.
+ *
+ * The buffer is placed on the transaction's metadata list and is marked
+ * as belonging to the transaction.  
+ *
+ * Special care needs to be taken if the buffer already belongs to the
+ * current committing transaction (in which case we should have frozen
+ * data present for that commit).  In that case, we don't relink the
+ * buffer: that only gets done when the old transaction finally
+ * completes its commit.
+ * 
+ * Returns error number or 0 on success.  
+ */
+
+int journal_dirty_metadata (handle_t *handle, struct buffer_head *bh)
+{
+	transaction_t *transaction = handle->h_transaction;
+	journal_t *journal = transaction->t_journal;
+	struct journal_head *jh = bh2jh(bh);
+
+	jbd_debug(5, "journal_head %p\n", jh);
+	JBUFFER_TRACE(jh, "entry");
+	lock_journal(journal);
+	if (is_handle_aborted(handle))
+		goto out_unlock;
+	
+	spin_lock(&journal_datalist_lock);
+	set_bit(BH_JBDDirty, &bh->b_state);
+	set_buffer_flushtime(bh);
+
+	J_ASSERT_JH(jh, jh->b_transaction != NULL);
+	
+	/* 
+	 * Metadata already on the current transaction list doesn't
+	 * need to be filed.  Metadata on another transaction's list must
+	 * be committing, and will be refiled once the commit completes:
+	 * leave it alone for now. 
+	 */
+
+	if (jh->b_transaction != transaction) {
+		JBUFFER_TRACE(jh, "already on other transaction");
+		J_ASSERT_JH(jh, jh->b_transaction ==
+					journal->j_committing_transaction);
+		J_ASSERT_JH(jh, jh->b_next_transaction == transaction);
+		/* And this case is illegal: we can't reuse another
+		 * transaction's data buffer, ever. */
+		/* FIXME: writepage() should be journalled */
+		J_ASSERT_JH(jh, jh->b_jlist != BJ_SyncData);
+		goto done_locked;
+	}
+
+	/* That test should have eliminated the following case: */
+	J_ASSERT_JH(jh, jh->b_frozen_data == 0);
+
+	JBUFFER_TRACE(jh, "file as BJ_Metadata");
+	__journal_file_buffer(jh, handle->h_transaction, BJ_Metadata);
+
+done_locked:
+	spin_unlock(&journal_datalist_lock);
+	JBUFFER_TRACE(jh, "exit");
+out_unlock:
+	unlock_journal(journal);
+	return 0;
+}
+
+#if 0
+/* 
+ * journal_release_buffer: undo a get_write_access without any buffer
+ * updates, if the update decided in the end that it didn't need access.
+ *
+ * journal_get_write_access() can block, so it is quite possible for a
+ * journaling component to decide after the write access is returned
+ * that global state has changed and the update is no longer required.  */
+
+void journal_release_buffer (handle_t *handle, struct buffer_head *bh)
+{
+	transaction_t *transaction = handle->h_transaction;
+	journal_t *journal = transaction->t_journal;
+	struct journal_head *jh = bh2jh(bh);
+
+	lock_journal(journal);
+	JBUFFER_TRACE(jh, "entry");
+
+	/* If the buffer is reserved but not modified by this
+	 * transaction, then it is safe to release it.  In all other
+	 * cases, just leave the buffer as it is. */
+
+	spin_lock(&journal_datalist_lock);
+	if (jh->b_jlist == BJ_Reserved && jh->b_transaction == transaction &&
+	    !buffer_jdirty(jh2bh(jh))) {
+		JBUFFER_TRACE(jh, "unused: refiling it");
+		handle->h_buffer_credits++;
+		__journal_refile_buffer(jh);
+	}
+	spin_unlock(&journal_datalist_lock);
+
+	JBUFFER_TRACE(jh, "exit");
+	unlock_journal(journal);
+}
+#endif
+
+/* 
+ * journal_forget: bforget() for potentially-journaled buffers.  We can
+ * only do the bforget if there are no commits pending against the
+ * buffer.  If the buffer is dirty in the current running transaction we
+ * can safely unlink it. 
+ *
+ * bh may not be a journalled buffer at all - it may be a non-JBD
+ * buffer which came off the hashtable.  Check for this.
+ *
+ * Decrements bh->b_count by one.
+ * 
+ * Allow this call even if the handle has aborted --- it may be part of
+ * the caller's cleanup after an abort.
+ */
+
+void journal_forget (handle_t *handle, struct buffer_head *bh)
+{
+	transaction_t *transaction = handle->h_transaction;
+	journal_t *journal = transaction->t_journal;
+	struct journal_head *jh;
+
+	BUFFER_TRACE(bh, "entry");
+
+	lock_journal(journal);
+	spin_lock(&journal_datalist_lock);
+
+	if (!buffer_jbd(bh))
+		goto not_jbd;
+	jh = bh2jh(bh);
+
+	if (jh->b_transaction == handle->h_transaction) {
+		J_ASSERT_JH(jh, !jh->b_frozen_data);
+
+		/* If we are forgetting a buffer which is already part
+		 * of this transaction, then we can just drop it from
+		 * the transaction immediately. */
+		clear_bit(BH_Dirty, &bh->b_state);
+		clear_bit(BH_JBDDirty, &bh->b_state);
+
+		JBUFFER_TRACE(jh, "belongs to current transaction: unfile");
+		J_ASSERT_JH(jh, !jh->b_committed_data);
+
+		__journal_unfile_buffer(jh);
+		jh->b_transaction = 0;
+
+		/* 
+		 * We are no longer going to journal this buffer.
+		 * However, the commit of this transaction is still
+		 * important to the buffer: the delete that we are now
+		 * processing might obsolete an old log entry, so by
+		 * committing, we can satisfy the buffer's checkpoint.
+		 *
+		 * So, if we have a checkpoint on the buffer, we should
+		 * now refile the buffer on our BJ_Forget list so that
+		 * we know to remove the checkpoint after we commit. 
+		 */
+
+		if (jh->b_cp_transaction) {
+			__journal_file_buffer(jh, transaction, BJ_Forget);
+		} else {
+			__journal_remove_journal_head(bh);
+			__brelse(bh);
+			if (!buffer_jbd(bh)) {
+				spin_unlock(&journal_datalist_lock);
+				unlock_journal(journal);
+				__bforget(bh);
+				return;
+			}
+		}
+		
+	} else if (jh->b_transaction) {
+		J_ASSERT_JH(jh, (jh->b_transaction == 
+				 journal->j_committing_transaction));
+		/* However, if the buffer is still owned by a prior
+		 * (committing) transaction, we can't drop it yet... */
+		JBUFFER_TRACE(jh, "belongs to older transaction");
+		/* ... but we CAN drop it from the new transaction if we
+		 * have also modified it since the original commit. */
+
+		if (jh->b_next_transaction) {
+			J_ASSERT(jh->b_next_transaction == transaction);
+			jh->b_next_transaction = NULL;
+		}
+	}
+
+not_jbd:
+	spin_unlock(&journal_datalist_lock);
+	unlock_journal(journal);
+	__brelse(bh);
+	return;
+}
+
+#if 0	/* Unused */
+/*
+ * journal_sync_buffer: flush a potentially-journaled buffer to disk.
+ *
+ * Used for O_SYNC filesystem operations.  If the buffer is journaled,
+ * we need to complete the O_SYNC by waiting for the transaction to
+ * complete.  It is an error to call journal_sync_buffer before
+ * journal_stop!
+ */
+
+void journal_sync_buffer(struct buffer_head *bh)
+{
+	transaction_t *transaction;
+	journal_t *journal;
+	long sequence;
+	struct journal_head *jh;
+
+	/* If the buffer isn't journaled, this is easy: just sync it to
+	 * disk.  */
+	BUFFER_TRACE(bh, "entry");
+
+	spin_lock(&journal_datalist_lock);
+	if (!buffer_jbd(bh)) {
+		spin_unlock(&journal_datalist_lock);
+		return;
+	}
+	jh = bh2jh(bh);
+	if (jh->b_transaction == NULL) {
+		/* If the buffer has already been journaled, then this
+		 * is a noop. */
+		if (jh->b_cp_transaction == NULL) {
+			spin_unlock(&journal_datalist_lock);
+			return;
+		}
+		atomic_inc(&bh->b_count);
+		spin_unlock(&journal_datalist_lock);
+		ll_rw_block (WRITE, 1, &bh);
+		wait_on_buffer(bh);
+		__brelse(bh);
+		goto out;
+	}
+	
+	/* Otherwise, just wait until the transaction is synced to disk. */
+	transaction = jh->b_transaction;
+	journal = transaction->t_journal;
+	sequence = transaction->t_tid;
+	spin_unlock(&journal_datalist_lock);
+
+	jbd_debug(2, "requesting commit for jh %p\n", jh);
+	log_start_commit (journal, transaction);
+	
+	while (tid_gt(sequence, journal->j_commit_sequence)) {
+		wake_up(&journal->j_wait_done_commit);
+		sleep_on(&journal->j_wait_done_commit);
+	}
+	JBUFFER_TRACE(jh, "exit");
+out:
+	return;
+}
+#endif
+
+/*
+ * All done for a particular handle.
+ *
+ * There is not much action needed here.  We just return any remaining
+ * buffer credits to the transaction and remove the handle.  The only
+ * complication is that we need to start a commit operation if the
+ * filesystem is marked for synchronous update.
+ *
+ * journal_stop itself will not usually return an error, but it may
+ * do so in unusual circumstances.  In particular, expect it to 
+ * return -EIO if a journal_abort has been executed since the
+ * transaction began.
+ */
+
+int journal_stop(handle_t *handle)
+{
+	transaction_t *transaction = handle->h_transaction;
+	journal_t *journal = transaction->t_journal;
+	int old_handle_count, err;
+	
+	if (!handle)
+		return 0;
+
+	J_ASSERT (transaction->t_updates > 0);
+	J_ASSERT (journal_current_handle() == handle);
+	
+	if (is_handle_aborted(handle))
+		err = -EIO;
+	else
+		err = 0;
+	
+	if (--handle->h_ref > 0) {
+		jbd_debug(4, "h_ref %d -> %d\n", handle->h_ref + 1,
+			  handle->h_ref);
+		return err;
+	}
+
+	jbd_debug(4, "Handle %p going down\n", handle);
+
+	/*
+	 * Implement synchronous transaction batching.  If the handle
+	 * was synchronous, don't force a commit immediately.  Let's
+	 * yield and let another thread piggyback onto this transaction.
+	 * Keep doing that while new threads continue to arrive.
+	 * It doesn't cost much - we're about to run a commit and sleep
+	 * on IO anyway.  Speeds up many-threaded, many-dir operations
+	 * by 30x or more...
+	 */
+	if (handle->h_sync) {
+		do {
+			old_handle_count = transaction->t_handle_count;
+			set_current_state(TASK_RUNNING);
+			current->policy |= SCHED_YIELD;
+			schedule();
+		} while (old_handle_count != transaction->t_handle_count);
+	}
+
+	current->journal_info = NULL;
+	transaction->t_outstanding_credits -= handle->h_buffer_credits;
+	transaction->t_updates--;
+	if (!transaction->t_updates) {
+		wake_up(&journal->j_wait_updates);
+		if (journal->j_barrier_count)
+			wake_up(&journal->j_wait_transaction_locked);
+	}
+
+	/* 
+	 * If the handle is marked SYNC, we need to set another commit
+	 * going!  We also want to force a commit if the current
+	 * transaction is occupying too much of the log, or if the
+	 * transaction is too old now.
+	 */
+	if (handle->h_sync ||
+			transaction->t_outstanding_credits >
+				journal->j_max_transaction_buffers ||
+	    		time_after_eq(jiffies, transaction->t_expires)) {
+		/* Do this even for aborted journals: an abort still
+		 * completes the commit thread, it just doesn't write
+		 * anything to disk. */
+		tid_t tid = transaction->t_tid;
+		
+		jbd_debug(2, "transaction too old, requesting commit for "
+					"handle %p\n", handle);
+		/* This is non-blocking */
+		log_start_commit(journal, transaction);
+		
+		/*
+		 * Special case: JFS_SYNC synchronous updates require us
+		 * to wait for the commit to complete.  
+		 */
+		if (handle->h_sync && !(current->flags & PF_MEMALLOC))
+			log_wait_commit(journal, tid);
+	}
+	kfree(handle);
+	return err;
+}
+
+/*
+ * For synchronous operations: force any uncommitted trasnactions
+ * to disk.  May seem kludgy, but it reuses all the handle batching
+ * code in a very simple manner.
+ */
+int journal_force_commit(journal_t *journal)
+{
+	handle_t *handle;
+	int ret = 0;
+
+	lock_kernel();
+	handle = journal_start(journal, 1);
+	if (IS_ERR(handle)) {
+		ret = PTR_ERR(handle);
+		goto out;
+	}
+	handle->h_sync = 1;
+	journal_stop(handle);
+out:
+	unlock_kernel();
+	return ret;
+}
+
+/*
+ *
+ * List management code snippets: various functions for manipulating the
+ * transaction buffer lists.
+ *
+ */
+
+/*
+ * Append a buffer to a transaction list, given the transaction's list head
+ * pointer.
+ * journal_datalist_lock is held.
+ */
+
+static inline void 
+__blist_add_buffer(struct journal_head **list, struct journal_head *jh)
+{
+	if (!*list) {
+		jh->b_tnext = jh->b_tprev = jh;
+		*list = jh;
+	} else {
+		/* Insert at the tail of the list to preserve order */
+		struct journal_head *first = *list, *last = first->b_tprev;
+		jh->b_tprev = last;
+		jh->b_tnext = first;
+		last->b_tnext = first->b_tprev = jh;
+	}
+}
+
+/* 
+ * Remove a buffer from a transaction list, given the transaction's list
+ * head pointer.
+ *
+ * Called with journal_datalist_lock held, and the journal may not
+ * be locked.
+ */
+
+static inline void
+__blist_del_buffer(struct journal_head **list, struct journal_head *jh)
+{
+	if (*list == jh) {
+		*list = jh->b_tnext;
+		if (*list == jh)
+			*list = 0;
+	}
+	jh->b_tprev->b_tnext = jh->b_tnext;
+	jh->b_tnext->b_tprev = jh->b_tprev;
+}
+
+/* 
+ * Remove a buffer from the appropriate transaction list.
+ *
+ * Note that this function can *change* the value of
+ * bh->b_transaction->t_sync_datalist, t_async_datalist, t_buffers, t_forget,
+ * t_iobuf_list, t_shadow_list, t_log_list or t_reserved_list.  If the caller
+ * is holding onto a copy of one of thee pointers, it could go bad.
+ * Generally the caller needs to re-read the pointer from the transaction_t.
+ *
+ * If bh->b_jlist is BJ_SyncData or BJ_AsyncData then we may have been called
+ * via journal_try_to_free_buffer() or journal_clean_data_list().  In that
+ * case, journal_datalist_lock will be held, and the journal may not be locked.
+ */
+void __journal_unfile_buffer(struct journal_head *jh)
+{
+	struct journal_head **list = 0;
+	transaction_t * transaction;
+
+	assert_spin_locked(&journal_datalist_lock);
+	transaction = jh->b_transaction;
+
+#ifdef __SMP__
+	J_ASSERT (current->lock_depth >= 0);
+#endif
+	J_ASSERT_JH(jh, jh->b_jlist < BJ_Types);
+
+	if (jh->b_jlist != BJ_None)
+		J_ASSERT_JH(jh, transaction != 0);
+
+	switch (jh->b_jlist) {
+	case BJ_None:
+		return;
+	case BJ_SyncData:
+		list = &transaction->t_sync_datalist;
+		break;
+	case BJ_AsyncData:
+		list = &transaction->t_async_datalist;
+		break;
+	case BJ_Metadata:
+		transaction->t_nr_buffers--;
+		J_ASSERT_JH(jh, transaction->t_nr_buffers >= 0);
+		list = &transaction->t_buffers;
+		break;
+	case BJ_Forget:
+		list = &transaction->t_forget;
+		break;
+	case BJ_IO:
+		list = &transaction->t_iobuf_list;
+		break;
+	case BJ_Shadow:
+		list = &transaction->t_shadow_list;
+		break;
+	case BJ_LogCtl:
+		list = &transaction->t_log_list;
+		break;
+	case BJ_Reserved:
+		list = &transaction->t_reserved_list;
+		break;
+	}
+	
+	__blist_del_buffer(list, jh);
+	jh->b_jlist = BJ_None;
+	if (test_and_clear_bit(BH_JBDDirty, &jh2bh(jh)->b_state)) {
+		set_bit(BH_Dirty, &jh2bh(jh)->b_state);
+	}
+}
+
+void journal_unfile_buffer(struct journal_head *jh)
+{
+	spin_lock(&journal_datalist_lock);
+	__journal_unfile_buffer(jh);
+	spin_unlock(&journal_datalist_lock);
+}
+
+/*
+ * Called from journal_try_to_free_buffers().  The journal is not
+ * locked. lru_list_lock is not held.
+ *
+ * Here we see why journal_datalist_lock is global and not per-journal.
+ * We cannot get back to this buffer's journal pointer without locking
+ * out journal_clean_data_list() in some manner.
+ *
+ * One could use journal_datalist_lock to get unracy access to a
+ * per-journal lock.
+ *
+ * Called with journal_datalist_lock held.
+ *
+ * Returns non-zero iff we were able to free the journal_head.
+ */
+static int __journal_try_to_free_buffer(struct buffer_head *bh,
+					int *locked_or_dirty)
+{
+	struct journal_head *jh;
+
+	assert_spin_locked(&journal_datalist_lock);
+
+	if (!buffer_jbd(bh))
+		return 1;
+	jh = bh2jh(bh);
+
+	if (buffer_locked(bh) || buffer_dirty(bh)) {
+		*locked_or_dirty = 1;
+		goto out;
+	}
+
+	if (!buffer_uptodate(bh))
+		goto out;
+
+	if (jh->b_next_transaction != 0)
+		goto out;
+
+	if (jh->b_transaction != 0 && jh->b_cp_transaction == 0) {
+		if (jh->b_jlist == BJ_SyncData || jh->b_jlist==BJ_AsyncData) {
+			/* A written-back ordered data buffer */
+			JBUFFER_TRACE(jh, "release data");
+			__journal_unfile_buffer(jh);
+			jh->b_transaction = 0;
+			__journal_remove_journal_head(bh);
+			__brelse(bh);
+		}
+	}
+	else if (jh->b_cp_transaction != 0 && jh->b_transaction == 0) {
+		/* written-back checkpointed metadata buffer */
+		if (jh->b_jlist == BJ_None) {
+			JBUFFER_TRACE(jh, "remove from checkpoint list");
+			__journal_remove_checkpoint(jh);
+			__journal_remove_journal_head(bh);
+			__brelse(bh);
+		}
+	}
+	return !buffer_jbd(bh);
+
+out:
+	return 0;
+}
+
+/*
+ * journal_try_to_free_buffers().  For all the buffers on this page,
+ * if they are fully written out ordered data, move them onto BUF_CLEAN
+ * so try_to_free_buffers() can reap them.  Called with lru_list_lock
+ * not held.  Does its own locking.
+ *
+ * This complicates JBD locking somewhat.  We aren't protected by the
+ * BKL here.  We wish to remove the buffer from its committing or
+ * running transaction's ->t_datalist via __journal_unfile_buffer.
+ *
+ * This may *change* the value of transaction_t->t_datalist, so anyone
+ * who looks at t_datalist needs to lock against this function.
+ *
+ * Even worse, someone may be doing a journal_dirty_data on this
+ * buffer.  So we need to lock against that.  journal_dirty_data()
+ * will come out of the lock with the buffer dirty, which makes it
+ * ineligible for release here.
+ *
+ * Who else is affected by this?  hmm...  Really the only contender
+ * is do_get_write_access() - it could be looking at the buffer while
+ * journal_try_to_free_buffer() is changing its state.  But that
+ * cannot happen because we never reallocate freed data as metadata
+ * while the data is part of a transaction.  Yes?
+ *
+ * This function returns non-zero if we wish try_to_free_buffers()
+ * to be called. We do this is the page is releasable by try_to_free_buffers().
+ * We also do it if the page has locked or dirty buffers and the caller wants
+ * us to perform sync or async writeout.
+ */
+int journal_try_to_free_buffers(journal_t *journal, 
+				struct page *page, int gfp_mask)
+{
+	struct buffer_head *bh;
+	struct buffer_head *tmp;
+	int locked_or_dirty = 0;
+	int call_ttfb = 1;
+
+	J_ASSERT(PageLocked(page));
+
+	bh = page->buffers;
+	tmp = bh;
+	spin_lock(&journal_datalist_lock);
+	do {
+		struct buffer_head *p = tmp;
+
+		tmp = tmp->b_this_page;
+		if (buffer_jbd(p))
+			if (!__journal_try_to_free_buffer(p, &locked_or_dirty))
+				call_ttfb = 0;
+	} while (tmp != bh);
+	spin_unlock(&journal_datalist_lock);
+
+	if (!(gfp_mask & (__GFP_IO|__GFP_WAIT)))
+		goto out;
+	if (!locked_or_dirty)
+		goto out;
+	/*
+	 * The VM wants us to do writeout, or to block on IO, or both.
+	 * So we allow try_to_free_buffers to be called even if the page
+	 * still has journalled buffers.
+	 */
+	call_ttfb = 1;
+out:
+	return call_ttfb;
+}
+
+/*
+ * This buffer is no longer needed.  If it is on an older transaction's
+ * checkpoint list we need to record it on this transaction's forget list
+ * to pin this buffer (and hence its checkpointing transaction) down until
+ * this transaction commits.  If the buffer isn't on a checkpoint list, we
+ * release it.
+ * Returns non-zero if JBD no longer has an interest in the buffer.
+ */
+static int dispose_buffer(struct journal_head *jh,
+		transaction_t *transaction)
+{
+	int may_free = 1;
+	struct buffer_head *bh = jh2bh(jh);
+
+	spin_lock(&journal_datalist_lock);
+	__journal_unfile_buffer(jh);
+	jh->b_transaction = 0;
+
+	if (jh->b_cp_transaction) {
+		JBUFFER_TRACE(jh, "on running+cp transaction");
+		__journal_file_buffer(jh, transaction, BJ_Forget);
+		clear_bit(BH_JBDDirty, &bh->b_state);
+		may_free = 0;
+	} else {
+		JBUFFER_TRACE(jh, "on running transaction");
+		__journal_remove_journal_head(bh);
+		__brelse(bh);
+	}
+	spin_unlock(&journal_datalist_lock);
+	return may_free;
+}
+
+/*
+ * journal_flushpage 
+ *
+ * This code is tricky.  It has a number of cases to deal with.
+ *
+ * There are two invariants which this code relies on:
+ *
+ * i_size must be updated on disk before we start calling flushpage on the
+ * data.
+ * 
+ *  This is done in ext3 by defining an ext3_setattr method which
+ *  updates i_size before truncate gets going.  By maintaining this
+ *  invariant, we can be sure that it is safe to throw away any buffers
+ *  attached to the current transaction: once the transaction commits,
+ *  we know that the data will not be needed.
+ * 
+ *  Note however that we can *not* throw away data belonging to the
+ *  previous, committing transaction!  
+ *
+ * Any disk blocks which *are* part of the previous, committing
+ * transaction (and which therefore cannot be discarded immediately) are
+ * not going to be reused in the new running transaction
+ *
+ *  The bitmap committed_data images guarantee this: any block which is
+ *  allocated in one transaction and removed in the next will be marked
+ *  as in-use in the committed_data bitmap, so cannot be reused until
+ *  the next transaction to delete the block commits.  This means that
+ *  leaving committing buffers dirty is quite safe: the disk blocks
+ *  cannot be reallocated to a different file and so buffer aliasing is
+ *  not possible.
+ *
+ *
+ * The above applies mainly to ordered data mode.  In writeback mode we
+ * don't make guarantees about the order in which data hits disk --- in
+ * particular we don't guarantee that new dirty data is flushed before
+ * transaction commit --- so it is always safe just to discard data
+ * immediately in that mode.  --sct 
+ */
+
+/*
+ * The journal_unmap_buffer helper function returns zero if the buffer
+ * concerned remains pinned as an anonymous buffer belonging to an older
+ * transaction.
+ *
+ * We're outside-transaction here.  Either or both of j_running_transaction
+ * and j_committing_transaction may be NULL.
+ */
+static int journal_unmap_buffer(journal_t *journal, struct buffer_head *bh)
+{
+	transaction_t *transaction;
+	struct journal_head *jh;
+	int may_free = 1;
+
+	BUFFER_TRACE(bh, "entry");
+
+	if (!buffer_mapped(bh))
+		return 1;
+
+	/* It is safe to proceed here without the
+	 * journal_datalist_spinlock because the buffers cannot be
+	 * stolen by try_to_free_buffers as long as we are holding the
+	 * page lock. --sct */
+
+	if (!buffer_jbd(bh))
+		goto zap_buffer;
+
+	jh = bh2jh(bh);
+	transaction = jh->b_transaction;
+	if (transaction == NULL) {
+		/* First case: not on any transaction.  If it
+		 * has no checkpoint link, then we can zap it:
+		 * it's a writeback-mode buffer so we don't care
+		 * if it hits disk safely. */
+		if (!jh->b_cp_transaction) {
+			JBUFFER_TRACE(jh, "not on any transaction: zap");
+			goto zap_buffer;
+		}
+		
+		if (!buffer_dirty(bh)) {
+			/* bdflush has written it.  We can drop it now */
+			goto zap_buffer;
+		}
+
+		/* OK, it must be in the journal but still not
+		 * written fully to disk: it's metadata or
+		 * journaled data... */
+
+		if (journal->j_running_transaction) {
+			/* ... and once the current transaction has
+			 * committed, the buffer won't be needed any
+			 * longer. */
+			JBUFFER_TRACE(jh, "checkpointed: add to BJ_Forget");
+			return dispose_buffer(jh,
+					journal->j_running_transaction);
+		} else {
+			/* There is no currently-running transaction. So the
+			 * orphan record which we wrote for this file must have
+			 * passed into commit.  We must attach this buffer to
+			 * the committing transaction, if it exists. */
+			if (journal->j_committing_transaction) {
+				JBUFFER_TRACE(jh, "give to committing trans");
+				return dispose_buffer(jh,
+					journal->j_committing_transaction);
+			} else {
+				/* The orphan record's transaction has
+				 * committed.  We can cleanse this buffer */
+				clear_bit(BH_JBDDirty, &bh->b_state);
+				goto zap_buffer;
+			}
+		}
+	} else if (transaction == journal->j_committing_transaction) {
+		/* If it is committing, we simply cannot touch it.  We
+		 * can remove it's next_transaction pointer from the
+		 * running transaction if that is set, but nothing
+		 * else. */
+		JBUFFER_TRACE(jh, "on committing transaction");
+		if (jh->b_next_transaction) {
+			J_ASSERT(jh->b_next_transaction ==
+					journal->j_running_transaction);
+			jh->b_next_transaction = NULL;
+		}
+		return 0;
+	} else {
+		/* Good, the buffer belongs to the running transaction.
+		 * We are writing our own transaction's data, not any
+		 * previous one's, so it is safe to throw it away
+		 * (remember that we expect the filesystem to have set
+		 * i_size already for this truncate so recovery will not
+		 * expose the disk blocks we are discarding here.) */
+		J_ASSERT_JH(jh, transaction == journal->j_running_transaction);
+		may_free = dispose_buffer(jh, transaction);
+	}
+
+zap_buffer:	
+	if (buffer_dirty(bh))
+		mark_buffer_clean(bh);
+	J_ASSERT_BH(bh, !buffer_jdirty(bh));
+	clear_bit(BH_Uptodate, &bh->b_state);
+	clear_bit(BH_Mapped, &bh->b_state);
+	clear_bit(BH_Req, &bh->b_state);
+	clear_bit(BH_New, &bh->b_state);
+	return may_free;
+}
+
+/*
+ * Return non-zero if the page's buffers were successfully reaped
+ */
+int journal_flushpage(journal_t *journal, 
+		      struct page *page, 
+		      unsigned long offset)
+{
+	struct buffer_head *head, *bh, *next;
+	unsigned int curr_off = 0;
+	int may_free = 1;
+		
+	if (!PageLocked(page))
+		BUG();
+	if (!page->buffers)
+		return 1;
+
+	/* We will potentially be playing with lists other than just the
+	 * data lists (especially for journaled data mode), so be
+	 * cautious in our locking. */
+	lock_journal(journal);
+
+	head = bh = page->buffers;
+	do {
+		unsigned int next_off = curr_off + bh->b_size;
+		next = bh->b_this_page;
+
+		/* AKPM: doing lock_buffer here may be overly paranoid */
+		if (offset <= curr_off) {
+		 	/* This block is wholly outside the truncation point */
+			lock_buffer(bh);
+			may_free &= journal_unmap_buffer(journal, bh);
+			unlock_buffer(bh);
+		}
+		curr_off = next_off;
+		bh = next;
+
+	} while (bh != head);
+
+	unlock_journal(journal);
+
+	if (!offset) {
+		if (!may_free || !try_to_free_buffers(page, 0))
+			return 0;
+		J_ASSERT(page->buffers == NULL);
+	}
+	return 1;
+}
+
+/* 
+ * File a buffer on the given transaction list. 
+ */
+void __journal_file_buffer(struct journal_head *jh,
+			transaction_t *transaction, int jlist)
+{
+	struct journal_head **list = 0;
+
+	assert_spin_locked(&journal_datalist_lock);
+	
+#ifdef __SMP__
+	J_ASSERT (current->lock_depth >= 0);
+#endif
+	J_ASSERT_JH(jh, jh->b_jlist < BJ_Types);
+	J_ASSERT_JH(jh, jh->b_transaction == transaction ||
+				jh->b_transaction == 0);
+
+	if (jh->b_transaction) {
+		if (jh->b_jlist == jlist)
+			return;
+		__journal_unfile_buffer(jh);
+	} else {
+		jh->b_transaction = transaction;
+	}
+
+	switch (jlist) {
+	case BJ_None:
+		J_ASSERT_JH(jh, !jh->b_committed_data);
+		J_ASSERT_JH(jh, !jh->b_frozen_data);
+		return;
+	case BJ_SyncData:
+		list = &transaction->t_sync_datalist;
+		break;
+	case BJ_AsyncData:
+		list = &transaction->t_async_datalist;
+		break;
+	case BJ_Metadata:
+		transaction->t_nr_buffers++;
+		list = &transaction->t_buffers;
+		break;
+	case BJ_Forget:
+		list = &transaction->t_forget;
+		break;
+	case BJ_IO:
+		list = &transaction->t_iobuf_list;
+		break;
+	case BJ_Shadow:
+		list = &transaction->t_shadow_list;
+		break;
+	case BJ_LogCtl:
+		list = &transaction->t_log_list;
+		break;
+	case BJ_Reserved:
+		list = &transaction->t_reserved_list;
+		break;
+	}
+
+	__blist_add_buffer(list, jh);
+	jh->b_jlist = jlist;
+
+	if (jlist == BJ_Metadata || jlist == BJ_Reserved || 
+	    jlist == BJ_Shadow || jlist == BJ_Forget) {
+		if (atomic_set_buffer_clean(jh2bh(jh))) {
+			set_bit(BH_JBDDirty, &jh2bh(jh)->b_state);
+		}
+	}
+}
+
+void journal_file_buffer(struct journal_head *jh,
+				transaction_t *transaction, int jlist)
+{
+	spin_lock(&journal_datalist_lock);
+	__journal_file_buffer(jh, transaction, jlist);
+	spin_unlock(&journal_datalist_lock);
+}
+
+/* 
+ * Remove a buffer from its current buffer list in preparation for
+ * dropping it from its current transaction entirely.  If the buffer has
+ * already started to be used by a subsequent transaction, refile the
+ * buffer on that transaction's metadata list.
+ */
+
+void __journal_refile_buffer(struct journal_head *jh)
+{
+	assert_spin_locked(&journal_datalist_lock);
+#ifdef __SMP__
+	J_ASSERT_JH(jh, current->lock_depth >= 0);
+#endif
+	__journal_unfile_buffer(jh);
+
+	/* If the buffer is now unused, just drop it.  If it has been
+	   modified by a later transaction, add it to the new
+	   transaction's metadata list. */
+
+	jh->b_transaction = jh->b_next_transaction;
+	jh->b_next_transaction = NULL;
+
+	if (jh->b_transaction != NULL) {
+		__journal_file_buffer(jh, jh->b_transaction, BJ_Metadata);
+		J_ASSERT_JH(jh, jh->b_transaction->t_state == T_RUNNING);
+	} else {
+		/* Onto BUF_DIRTY for writeback */
+		refile_buffer(jh2bh(jh));
+	}
+}
+
+/*
+ * For the unlocked version of this call, also make sure that any
+ * hanging journal_head is cleaned up if necessary.
+ *
+ * __journal_refile_buffer is usually called as part of a single locked
+ * operation on a buffer_head, in which the caller is probably going to
+ * be hooking the journal_head onto other lists.  In that case it is up
+ * to the caller to remove the journal_head if necessary.  For the
+ * unlocked journal_refile_buffer call, the caller isn't going to be
+ * doing anything else to the buffer so we need to do the cleanup
+ * ourselves to avoid a jh leak. 
+ *
+ * *** The journal_head may be freed by this call! ***
+ */
+void journal_refile_buffer(struct journal_head *jh)
+{
+	struct buffer_head *bh;
+
+	spin_lock(&journal_datalist_lock);
+	bh = jh2bh(jh);
+
+	__journal_refile_buffer(jh);
+	__journal_remove_journal_head(bh);
+
+	spin_unlock(&journal_datalist_lock);
+	__brelse(bh);
+}